#include "highlighters.hh"

#include "assert.hh"
#include "buffer_utils.hh"
#include "context.hh"
#include "containers.hh"
#include "display_buffer.hh"
#include "face_registry.hh"
#include "highlighter_group.hh"
#include "line_modification.hh"
#include "option_types.hh"
#include "parameters_parser.hh"
#include "register_manager.hh"
#include "string.hh"
#include "utf8.hh"
#include "utf8_iterator.hh"

#include <sstream>
#include <locale>

namespace Kakoune
{

template<typename T>
void highlight_range(DisplayBuffer& display_buffer,
                     ByteCoord begin, ByteCoord end,
                     bool skip_replaced, T func)
{
    if (begin == end or end <= display_buffer.range().first
                     or begin >= display_buffer.range().second)
        return;

    for (auto& line : display_buffer.lines())
    {
        auto& range = line.range();
        if (range.second <= begin or  end < range.first)
            continue;

        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            bool is_replaced = atom_it->type() == DisplayAtom::ReplacedBufferRange;

            if (not atom_it->has_buffer_range() or
                (skip_replaced and is_replaced))
                continue;

            if (end <= atom_it->begin() or begin >= atom_it->end())
                continue;

            if (not is_replaced and begin > atom_it->begin())
                atom_it = ++line.split(atom_it, begin);

            if (not is_replaced and end < atom_it->end())
            {
                atom_it = line.split(atom_it, end);
                func(*atom_it);
                ++atom_it;
            }
            else
                func(*atom_it);
        }
    }
}

void apply_highlighter(const Context& context,
                       HighlightFlags flags,
                       DisplayBuffer& display_buffer,
                       ByteCoord begin, ByteCoord end,
                       Highlighter& highlighter)
{
    if (begin == end)
        return;

    using LineIterator = DisplayBuffer::LineList::iterator;
    LineIterator first_line;
    Vector<DisplayLine::iterator> insert_pos;
    auto line_end = display_buffer.lines().end();

    DisplayBuffer region_display;
    auto& region_lines = region_display.lines();
    for (auto line_it = display_buffer.lines().begin(); line_it != line_end; ++line_it)
    {
        auto& line = *line_it;
        auto& range = line.range();
        if (range.second <= begin or end <= range.first)
            continue;

        if (region_lines.empty())
            first_line = line_it;
        region_lines.emplace_back();
        insert_pos.emplace_back();

        if (range.first < begin or range.second > end)
        {
            size_t beg_idx = 0;
            size_t end_idx = line.atoms().size();

            for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
            {
                if (not atom_it->has_buffer_range() or end <= atom_it->begin() or begin >= atom_it->end())
                    continue;

                bool is_replaced = atom_it->type() == DisplayAtom::ReplacedBufferRange;
                if (atom_it->begin() <= begin)
                {
                    if (is_replaced or atom_it->begin() == begin)
                        beg_idx = atom_it - line.begin();
                    else
                    {
                        atom_it = ++line.split(atom_it, begin);
                        beg_idx = atom_it - line.begin();
                        ++end_idx;
                    }
                }

                if (atom_it->end() >= end)
                {
                    if (is_replaced or atom_it->end() == end)
                        end_idx = atom_it - line.begin() + 1;
                    else
                    {
                        atom_it = ++line.split(atom_it, end);
                        end_idx = atom_it - line.begin();
                    }
                }
            }
            std::move(line.begin() + beg_idx, line.begin() + end_idx,
                      std::back_inserter(region_lines.back()));
            insert_pos.back() = line.erase(line.begin() + beg_idx, line.begin() + end_idx);
        }
        else
        {
            region_lines.back() = std::move(line);
            insert_pos.back() = line.begin();
        }
    }

    if (region_display.lines().empty())
        return;

    region_display.compute_range();
    highlighter.highlight(context, flags, region_display, {begin, end});

    for (size_t i = 0; i < region_lines.size(); ++i)
    {
        auto& line = *(first_line + i);
        auto pos = insert_pos[i];
        for (auto& atom : region_lines[i])
            pos = ++line.insert(pos, std::move(atom));
    }
    display_buffer.compute_range();
}

auto apply_face = [](const Face& face)
{
    return [&face](DisplayAtom& atom) {
        if (face.fg != Colors::Default)
            atom.face.fg = face.fg;
        if (face.bg != Colors::Default)
            atom.face.bg = face.bg;
        if (face.attributes != Attribute::Normal)
            atom.face.attributes |= face.attributes;
    };
};

static HighlighterAndId create_fill_highlighter(HighlighterParameters params)
{
    if (params.size() != 1)
        throw runtime_error("wrong parameter count");

    const String& facespec = params[0];
    get_face(facespec); // validate param

    auto func = [=](const Context& context, HighlightFlags flags,
                    DisplayBuffer& display_buffer, BufferRange range)
    {
        highlight_range(display_buffer, range.first, range.second, true,
                        apply_face(get_face(facespec)));
    };
    return {"fill_" + facespec, make_simple_highlighter(std::move(func))};
}

template<typename T>
struct BufferSideCache
{
    BufferSideCache() : m_id{ValueId::get_free_id()} {}

    T& get(const Buffer& buffer)
    {
        Value& cache_val = buffer.values()[m_id];
        if (not cache_val)
            cache_val = Value(T{});
        return cache_val.as<T>();
    }
private:
    ValueId m_id;
};

static bool overlaps(const BufferRange& lhs, const BufferRange& rhs)
{
    return lhs.first < rhs.first ? lhs.second > rhs.first
                                 : rhs.second > lhs.first;
}

using FacesSpec = Vector<std::pair<size_t, String>, MemoryDomain::Highlight>;

class RegexHighlighter : public Highlighter
{
public:
    RegexHighlighter(Regex regex, FacesSpec faces)
        : m_regex{std::move(regex)}, m_faces{std::move(faces)}
    {
        ensure_first_face_is_capture_0();
    }

    void highlight(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange range) override
    {
        if (flags != HighlightFlags::Highlight or not overlaps(display_buffer.range(), range))
            return;

        Vector<Face> faces(m_faces.size());
        for (int f = 0; f < m_faces.size(); ++f)
        {
            if (not m_faces[f].second.empty())
                faces[f] = get_face(m_faces[f].second);
        }

        auto& matches = get_matches(context.buffer(), display_buffer.range(), range);
        kak_assert(matches.size() % m_faces.size() == 0);
        for (size_t m = 0; m < matches.size(); ++m)
        {
            auto& face = faces[m % faces.size()];
            if (face == Face{})
                continue;

            highlight_range(display_buffer,
                            matches[m].first, matches[m].second,
                            true, apply_face(face));
        }
    }

    void reset(Regex regex, FacesSpec faces)
    {
        m_regex = std::move(regex);
        m_faces = std::move(faces);
        ensure_first_face_is_capture_0();
        ++m_regex_version;
    }

    static HighlighterAndId create(HighlighterParameters params)
    {
        if (params.size() < 2)
            throw runtime_error("wrong parameter count");

        try
        {
            static Regex face_spec_ex(R"((\d+):(.*))");
            FacesSpec faces;
            for (auto it = params.begin() + 1;  it != params.end(); ++it)
            {
                MatchResults<String::const_iterator> res;
                if (not regex_match(it->begin(), it->end(), res, face_spec_ex))
                    throw runtime_error("wrong face spec: '" + *it +
                                         "' expected <capture>:<facespec>");
                get_face({res[2].first, res[2].second}); // throw if wrong face spec
                int capture = str_to_int({res[1].first, res[1].second});
                faces.emplace_back(capture, String{res[2].first, res[2].second});
            }

            String id = "hlregex'" + params[0] + "'";

            Regex ex{params[0].begin(), params[0].end(), Regex::optimize};

            return {id, make_unique<RegexHighlighter>(std::move(ex),
                                                      std::move(faces))};
        }
        catch (RegexError& err)
        {
            throw runtime_error(String("regex error: ") + err.what());
        }
    }

private:
    // stores the range for each highlighted capture of each match
    using MatchList = Vector<BufferRange, MemoryDomain::Highlight>;
    struct Cache
    {
        size_t m_timestamp = -1;
        size_t m_regex_version = -1;
        using RangeAndMatches = std::pair<BufferRange, MatchList>;
        Vector<RangeAndMatches, MemoryDomain::Highlight> m_matches;
    };
    BufferSideCache<Cache> m_cache;

    Regex     m_regex;
    FacesSpec m_faces;

    size_t m_regex_version = 0;

    void ensure_first_face_is_capture_0()
    {
        if (m_faces.empty())
            return;

        std::sort(m_faces.begin(), m_faces.end(),
                  [](const std::pair<size_t, String>& lhs,
                     const std::pair<size_t, String>& rhs)
                  { return lhs.first < rhs.first; });
        if (m_faces[0].first != 0)
            m_faces.emplace(m_faces.begin(), 0, String{});
    }

    void add_matches(const Buffer& buffer, MatchList& matches,
                     BufferRange range)
    {
        kak_assert(matches.size() % m_faces.size() == 0);
        using RegexIt = RegexIterator<BufferIterator>;
        RegexIt re_it{buffer.iterator_at(range.first),
                      buffer.iterator_at(range.second), m_regex};
        RegexIt re_end;
        for (; re_it != re_end; ++re_it)
        {
            for (size_t i = 0; i < m_faces.size(); ++i)
            {
                auto& sub = (*re_it)[m_faces[i].first];
                matches.emplace_back(sub.first.coord(), sub.second.coord());
            }
        }
    }

    MatchList& get_matches(const Buffer& buffer, BufferRange display_range,
                           BufferRange buffer_range)
    {
        Cache& cache = m_cache.get(buffer);
        auto& matches = cache.m_matches;

        if (cache.m_regex_version != m_regex_version or
            cache.m_timestamp != buffer.timestamp())
        {
            matches.clear();
            cache.m_timestamp = buffer.timestamp();
            cache.m_regex_version = m_regex_version;
        }
        const LineCount line_offset = 3;
        BufferRange range{std::max<ByteCoord>(buffer_range.first, display_range.first.line - line_offset),
                          std::min<ByteCoord>(buffer_range.second, display_range.second.line + line_offset)};

        auto it = std::upper_bound(matches.begin(), matches.end(), range,
                                   [](const BufferRange& lhs, const Cache::RangeAndMatches& rhs)
                                   { return lhs.first < rhs.first.second; });

        if (it == matches.end() or it->first.first > range.second)
        {
            it = matches.insert(it, Cache::RangeAndMatches{range, {}});
            add_matches(buffer, it->second, range);
        }
        else if (it->second.empty())
        {
            it->first = range;
            add_matches(buffer, it->second, range);
        }
        else
        {
            // Here we extend the matches, that is not strictly valid,
            // but may work nicely with every reasonable regex, and
            // greatly reduces regex parsing. To change if we encounter
            // regex that do not work great with that.
            BufferRange& old_range = it->first;
            MatchList& matches = it->second;

            // Thanks to the ensure_first_face_is_capture_0 method, we know
            // these point to the first/last matches capture 0.
            auto first_end = matches.begin()->second;
            auto last_begin = (matches.end() - m_faces.size())->first;

            bool remove_last = true;

            // add regex matches from new begin to old first match end
            if (range.first < old_range.first)
            {
                old_range.first = range.first;
                MatchList new_matches;
                add_matches(buffer, new_matches, {range.first, first_end});
                matches.erase(matches.begin(), matches.begin() + m_faces.size());

                // first matches was last matches as well, so
                // make sure we do not try to remove them again.
                if (matches.empty())
                    remove_last = false;

                std::copy(std::make_move_iterator(new_matches.begin()),
                          std::make_move_iterator(new_matches.end()),
                          std::inserter(matches, matches.begin()));
            }
            // add regex matches from old last match begin to new end
            if (old_range.second < range.second)
            {
                old_range.second = range.second;
                if (remove_last)
                    matches.erase(matches.end() - m_faces.size(), matches.end());
                add_matches(buffer, matches, {last_begin, range.second});
            }
        }
        return it->second;
    }
};

template<typename RegexGetter, typename FaceGetter>
class DynamicRegexHighlighter : public Highlighter
{
public:
    DynamicRegexHighlighter(RegexGetter regex_getter, FaceGetter face_getter)
        : m_regex_getter(std::move(regex_getter)),
          m_face_getter(std::move(face_getter)),
          m_highlighter(Regex(), FacesSpec{}) {}

    void highlight(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange range)
    {
        if (flags != HighlightFlags::Highlight)
            return;

        Regex regex = m_regex_getter(context);
        FacesSpec face = m_face_getter(context);
        if (regex != m_last_regex or face != m_last_face)
        {
            m_last_regex = regex;
            m_last_face = face;
            if (not m_last_regex.empty())
                m_highlighter.reset(m_last_regex, m_last_face);
        }
        if (not m_last_regex.empty() and not m_last_face.empty())
            m_highlighter.highlight(context, flags, display_buffer, range);
    }

private:
    Regex       m_last_regex;
    RegexGetter m_regex_getter;

    FacesSpec   m_last_face;
    FaceGetter  m_face_getter;

    RegexHighlighter m_highlighter;
};

template<typename RegexGetter, typename FaceGetter>
std::unique_ptr<DynamicRegexHighlighter<RegexGetter, FaceGetter>>
make_dynamic_regex_highlighter(RegexGetter regex_getter, FaceGetter face_getter)
{
    return make_unique<DynamicRegexHighlighter<RegexGetter, FaceGetter>>(
        std::move(regex_getter), std::move(face_getter));
}


HighlighterAndId create_search_highlighter(HighlighterParameters params)
{
    if (params.size() != 0)
        throw runtime_error("wrong parameter count");
        auto get_face = [](const Context& context){
            return FacesSpec{ { 0, "Search" } };
        };
        auto get_regex = [](const Context& context){
            auto s = context.main_sel_register_value("/");
            try
            {
                return s.empty() ? Regex{} : Regex{s.begin(), s.end()};
            }
            catch (RegexError& err)
            {
                return Regex{};
            }
        };
        return {"hlsearch", make_dynamic_regex_highlighter(get_regex, get_face)};
}

HighlighterAndId create_regex_option_highlighter(HighlighterParameters params)
{
    if (params.size() != 2)
        throw runtime_error("wrong parameter count");

    String facespec = params[1];
    auto get_face = [=](const Context&){
        return FacesSpec{ { 0, facespec } };
    };

    String option_name = params[0];
    // verify option type now
    GlobalScope::instance().options()[option_name].get<Regex>();

    auto get_regex = [option_name](const Context& context){
        return context.options()[option_name].get<Regex>();
    };
    return {"hloption_" + option_name, make_dynamic_regex_highlighter(get_regex, get_face)};
}

HighlighterAndId create_line_option_highlighter(HighlighterParameters params)
{
    if (params.size() != 2)
        throw runtime_error("wrong parameter count");

    String facespec = params[1];
    String option_name = params[0];

    get_face(facespec); // validate facespec
    GlobalScope::instance().options()[option_name].get<int>(); // verify option type now

    auto func = [=](const Context& context, HighlightFlags flags,
                    DisplayBuffer& display_buffer, BufferRange)
    {
        int line = context.options()[option_name].get<int>();
        highlight_range(display_buffer, {line-1, 0}, {line, 0}, false,
                        apply_face(get_face(facespec)));
    };

    return {"hlline_" + params[0], make_simple_highlighter(std::move(func))};
}

void expand_tabulations(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange)
{
    const int tabstop = context.options()["tabstop"].get<int>();
    auto& buffer = context.buffer();
    for (auto& line : display_buffer.lines())
    {
        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            if (atom_it->type() != DisplayAtom::BufferRange)
                continue;

            auto begin = buffer.iterator_at(atom_it->begin());
            auto end = buffer.iterator_at(atom_it->end());
            for (BufferIterator it = begin; it != end; ++it)
            {
                if (*it == '\t')
                {
                    if (it != begin)
                        atom_it = ++line.split(atom_it, it.coord());
                    if (it+1 != end)
                        atom_it = line.split(atom_it, (it+1).coord());

                    int column = (int)get_column(buffer, tabstop, it.coord());
                    int count = tabstop - (column % tabstop);
                    String padding;
                    for (int i = 0; i < count; ++i)
                        padding += ' ';
                    atom_it->replace(padding);
                    break;
                }
            }
        }
    }
}

void show_whitespaces(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange)
{
    const int tabstop = context.options()["tabstop"].get<int>();
    auto& buffer = context.buffer();
    for (auto& line : display_buffer.lines())
    {
        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            if (atom_it->type() != DisplayAtom::BufferRange)
                continue;

            auto begin = buffer.iterator_at(atom_it->begin());
            auto end = buffer.iterator_at(atom_it->end());
            for (BufferIterator it = begin; it != end; ++it)
            {
                auto c = *it;
                if (c == '\t' or c == ' ' or c == '\n')
                {
                    if (it != begin)
                        atom_it = ++line.split(atom_it, it.coord());
                    if (it+1 != end)
                        atom_it = line.split(atom_it, (it+1).coord());

                    if (c == '\t')
                    {
                        int column = (int)get_column(buffer, tabstop, it.coord());
                        int count = tabstop - (column % tabstop);
                        String padding = "→";
                        for (int i = 0; i < count-1; ++i)
                            padding += ' ';
                        atom_it->replace(padding);
                    }
                    else if (c == ' ')
                        atom_it->replace("·");
                    else if (c == '\n')
                        atom_it->replace("¬");
                    break;
                }
            }
        }
    }
}

template<bool relative, bool hl_cursor_line>
void show_line_numbers(const Context& context, HighlightFlags flags,
                       DisplayBuffer& display_buffer, BufferRange)
{
    const Face face = get_face("LineNumbers");
    const Face face_absolute = get_face("LineNumberCursor");
    LineCount last_line = context.buffer().line_count();
    int digit_count = 0;
    for (LineCount c = last_line; c > 0; c /= 10)
        ++digit_count;

    char format[] = "%?d│";
    format[1] = '0' + digit_count + (relative ? 1 : 0);
    int main_selection = (int)context.selections().main().cursor().line + 1;
    for (auto& line : display_buffer.lines())
    {
        const int current_line = (int)line.range().first.line + 1;
        const bool is_cursor_line = main_selection == current_line;
        const int line_to_format = (relative and not is_cursor_line) ?
                                   current_line - main_selection : current_line;
        char buffer[16];
        snprintf(buffer, 16, format, line_to_format);
        DisplayAtom atom{buffer};
        atom.face = (hl_cursor_line and is_cursor_line) ? face_absolute : face;
        line.insert(line.begin(), std::move(atom));
    }
}

HighlighterAndId number_lines_factory(HighlighterParameters params)
{
    static const ParameterDesc param_desc{
        { { "relative", { false, "" } },
          { "hlcursor", { false, "" } } },
        ParameterDesc::Flags::None, 0, 0
    };
    ParametersParser parser(params, param_desc);

    constexpr struct {
        StringView name;
        void (*func)(const Context&, HighlightFlags, DisplayBuffer&, BufferRange);
    } funcs[] = {
        { "number_lines", show_line_numbers<false, false> },
        { "number_lines", show_line_numbers<false, true> },
        { "number_lines_relative", show_line_numbers<true, false> },
        { "number_lines_relative", show_line_numbers<true, true> },
    };
    const int index = (parser.get_switch("relative") ? 1 : 0) * 2 +
                      (parser.get_switch("hlcursor") ? 1 : 0);

    return {funcs[index].name.str(), make_simple_highlighter(funcs[index].func)};
}

void show_matching_char(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange)
{
    const Face face = get_face("MatchingChar");
    using CodepointPair = std::pair<Codepoint, Codepoint>;
    static const CodepointPair matching_chars[] = { { '(', ')' }, { '{', '}' }, { '[', ']' }, { '<', '>' } };
    const auto range = display_buffer.range();
    const auto& buffer = context.buffer();
    for (auto& sel : context.selections())
    {
        auto pos = sel.cursor();
        if (pos < range.first or pos >= range.second)
            continue;
        auto c = buffer.byte_at(pos);
        for (auto& pair : matching_chars)
        {
            int level = 1;
            if (c == pair.first)
            {
                for (auto it = buffer.iterator_at(pos)+1,
                         end = buffer.iterator_at(range.second); it != end; ++it)
                {
                    char c = *it;
                    if (c == pair.first)
                        ++level;
                    else if (c == pair.second and --level == 0)
                    {
                        highlight_range(display_buffer, it.coord(), (it+1).coord(), false,
                                        apply_face(face));
                        break;
                    }
                }
            }
            else if (c == pair.second and pos > range.first)
            {
                for (auto it = buffer.iterator_at(pos)-1,
                         end = buffer.iterator_at(range.first); true; --it)
                {
                    char c = *it;
                    if (c == pair.second)
                        ++level;
                    else if (c == pair.first and --level == 0)
                    {
                        highlight_range(display_buffer, it.coord(), (it+1).coord(), false,
                                        apply_face(face));
                        break;
                    }
                    if (it == end)
                        break;
                }
            }
        }
    }
}

void highlight_selections(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange)
{
    if (flags != HighlightFlags::Highlight)
        return;
    const auto& buffer = context.buffer();
    for (size_t i = 0; i < context.selections().size(); ++i)
    {
        auto& sel = context.selections()[i];
        const bool forward = sel.anchor() <= sel.cursor();
        ByteCoord begin = forward ? sel.anchor() : buffer.char_next(sel.cursor());
        ByteCoord end   = forward ? (ByteCoord)sel.cursor() : buffer.char_next(sel.anchor());

        const bool primary = (i == context.selections().main_index());
        Face sel_face = get_face(primary ? "PrimarySelection" : "SecondarySelection");
        highlight_range(display_buffer, begin, end, false,
                        apply_face(sel_face));
    }
    for (size_t i = 0; i < context.selections().size(); ++i)
    {
        auto& sel = context.selections()[i];
        const bool primary = (i == context.selections().main_index());
        Face cur_face = get_face(primary ? "PrimaryCursor" : "SecondaryCursor");
        highlight_range(display_buffer, sel.cursor(), buffer.char_next(sel.cursor()), false,
                        apply_face(cur_face));
    }
}

void expand_unprintable(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange)
{
    auto& buffer = context.buffer();
    for (auto& line : display_buffer.lines())
    {
        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            if (atom_it->type() == DisplayAtom::BufferRange)
            {
                for (auto it  = buffer.iterator_at(atom_it->begin()),
                          end = buffer.iterator_at(atom_it->end()); it < end;)
                {
                    Codepoint cp = utf8::codepoint<utf8::InvalidPolicy::Pass>(it, end);
                    auto next = utf8::next(it, end);
                    if (cp != '\n' and not iswprint(cp))
                    {
                        std::ostringstream oss;
                        oss << "U+" << std::hex << cp;
                        const auto& stdstr = oss.str();
                        String str{stdstr.begin(), stdstr.end()};
                        if (it.coord() != atom_it->begin())
                            atom_it = ++line.split(atom_it, it.coord());
                        if (next.coord() < atom_it->end())
                            atom_it = line.split(atom_it, next.coord());
                        atom_it->replace(str);
                        atom_it->face = { Colors::Red, Colors::Black };
                        break;
                    }
                    it = next;
                }
            }
        }
    }
}

HighlighterAndId create_flag_lines_highlighter(HighlighterParameters params)
{
    if (params.size() != 2)
        throw runtime_error("wrong parameter count");

    const String& option_name = params[1];
    Color bg = str_to_color(params[0]);

    // throw if wrong option type
    GlobalScope::instance().options()[option_name].get<Vector<LineAndFlag, MemoryDomain::Options>>();

    auto func = [=](const Context& context, HighlightFlags flags,
                    DisplayBuffer& display_buffer, BufferRange)
    {
        auto& lines_opt = context.options()[option_name];
        auto& lines = lines_opt.get<Vector<LineAndFlag, MemoryDomain::Options>>();

        CharCount width = 0;
        for (auto& l : lines)
             width = std::max(width, std::get<2>(l).char_length());
        const String empty{' ', width};
        for (auto& line : display_buffer.lines())
        {
            int line_num = (int)line.range().first.line + 1;
            auto it = find_if(lines,
                              [&](const LineAndFlag& l)
                              { return std::get<0>(l) == line_num; });
            String content = it != lines.end() ? std::get<2>(*it) : empty;
            content += String(' ', width - content.char_length());
            DisplayAtom atom{std::move(content)};
            atom.face = { it != lines.end() ? std::get<1>(*it) : Colors::Default , bg };
            line.insert(line.begin(), std::move(atom));
        }
    };

    return {"hlflags_" + params[1], make_simple_highlighter(func) };
}

HighlighterAndId create_highlighter_group(HighlighterParameters params)
{
    if (params.size() != 1)
        throw runtime_error("wrong parameter count");

    return HighlighterAndId(params[0], make_unique<HighlighterGroup>());
}

HighlighterAndId create_reference_highlighter(HighlighterParameters params)
{
    if (params.size() != 1)
        throw runtime_error("wrong parameter count");

    const String& name = params[0];

    // throw if not found
    //DefinedHighlighters::instance().get_group(name, '/');

    auto func = [=](const Context& context, HighlightFlags flags,
                    DisplayBuffer& display_buffer, BufferRange range)
    {
        try
        {
            DefinedHighlighters::instance().get_child(name).highlight(context, flags, display_buffer, range);
        }
        catch (child_not_found&)
        {}
    };

    return {name, make_simple_highlighter(func)};
}

struct RegexMatch
{
    LineCount line;
    ByteCount begin;
    ByteCount end;

    ByteCoord begin_coord() const { return { line, begin }; }
    ByteCoord end_coord() const { return { line, end }; }
};
using RegexMatchList = Vector<RegexMatch, MemoryDomain::Highlight>;

void find_matches(const Buffer& buffer, RegexMatchList& matches, const Regex& regex)
{
    for (auto line = 0_line, end = buffer.line_count(); line < end; ++line)
    {
        auto l = buffer[line];
        for (RegexIterator<const char*> it{l.begin(), l.end(), regex}, end{}; it != end; ++it)
        {
            ByteCount b = (int)((*it)[0].first - l.begin());
            ByteCount e = (int)((*it)[0].second - l.begin());
            matches.push_back({ line, b, e });
        }
    }
}

void update_matches(const Buffer& buffer, ConstArrayView<LineModification> modifs,
                    RegexMatchList& matches, const Regex& regex)
{
    // remove out of date matches and update line for others
    auto ins_pos = matches.begin();
    for (auto it = ins_pos; it != matches.end(); ++it)
    {
        auto modif_it = std::upper_bound(modifs.begin(), modifs.end(), it->line,
                                         [](const LineCount& l, const LineModification& c)
                                         { return l < c.old_line; });

        if (modif_it != modifs.begin())
        {
            auto& prev = *(modif_it-1);
            if (it->line < prev.old_line + prev.num_removed)
                continue; // match removed

            it->line += prev.diff();
        }

        kak_assert(buffer.is_valid(it->begin_coord()) or
                   buffer[it->line].length() == it->begin);
        kak_assert(buffer.is_valid(it->end_coord()) or
                   buffer[it->line].length() == it->end);

        if (ins_pos != it)
            *ins_pos = std::move(*it);
        ++ins_pos;
    }
    matches.erase(ins_pos, matches.end());
    size_t pivot = matches.size();

    // try to find new matches in each updated lines
    for (auto& modif : modifs)
    {
        for (auto line = modif.new_line; line < modif.new_line + modif.num_added; ++line)
        {
            auto l = buffer[line];
            for (RegexIterator<const char*> it{l.begin(), l.end(), regex}, end{}; it != end; ++it)
            {
                ByteCount b = (int)((*it)[0].first - l.begin());
                ByteCount e = (int)((*it)[0].second - l.begin());
                matches.push_back({ line, b, e });
            }
        }
    }
    std::inplace_merge(matches.begin(), matches.begin() + pivot, matches.end(),
                       [](const RegexMatch& lhs, const RegexMatch& rhs) {
                           return lhs.begin_coord() < rhs.begin_coord();
                       });
}

struct RegionMatches
{
    RegexMatchList begin_matches;
    RegexMatchList end_matches;
    RegexMatchList recurse_matches;

    static bool compare_to_begin(const RegexMatch& lhs, ByteCoord rhs)
    {
        return lhs.begin_coord() < rhs;
    }

    RegexMatchList::const_iterator find_next_begin(ByteCoord pos) const
    {
        return std::lower_bound(begin_matches.begin(), begin_matches.end(),
                                pos, compare_to_begin);
    }

    RegexMatchList::const_iterator find_matching_end(ByteCoord beg_pos) const
    {
        auto end_it = end_matches.begin();
        auto rec_it = recurse_matches.begin();
        int recurse_level = 0;
        while (true)
        {
            end_it = std::lower_bound(end_it, end_matches.end(),
                                      beg_pos, compare_to_begin);
            rec_it = std::lower_bound(rec_it, recurse_matches.end(),
                                      beg_pos, compare_to_begin);

            if (end_it == end_matches.end())
                return end_it;

            while (rec_it != recurse_matches.end() and
                   rec_it->end_coord() <= end_it->begin_coord())
            {
                ++recurse_level;
                ++rec_it;
            }

            if (recurse_level == 0)
                return end_it;

            --recurse_level;
            beg_pos = end_it->end_coord();
        }
    }
};

struct RegionDesc
{
    Regex m_begin;
    Regex m_end;
    Regex m_recurse;

    RegionMatches find_matches(const Buffer& buffer) const
    {
        RegionMatches res;
        Kakoune::find_matches(buffer, res.begin_matches, m_begin);
        Kakoune::find_matches(buffer, res.end_matches, m_end);
        if (not m_recurse.empty())
            Kakoune::find_matches(buffer, res.recurse_matches, m_recurse);
        return res;
    }

    void update_matches(const Buffer& buffer,
                        ConstArrayView<LineModification> modifs,
                        RegionMatches& matches) const
    {
        Kakoune::update_matches(buffer, modifs, matches.begin_matches, m_begin);
        Kakoune::update_matches(buffer, modifs, matches.end_matches, m_end);
        if (not m_recurse.empty())
            Kakoune::update_matches(buffer, modifs, matches.recurse_matches, m_recurse);
    }
};

struct RegionsHighlighter : public Highlighter
{
public:
    using NamedRegionDescList = Vector<std::pair<String, RegionDesc>, MemoryDomain::Highlight>;

    RegionsHighlighter(NamedRegionDescList regions, String default_group)
        : m_regions{std::move(regions)}, m_default_group{std::move(default_group)}
    {
        if (m_regions.empty())
            throw runtime_error("at least one region must be defined");

        for (auto& region : m_regions)
        {
            m_groups.append({region.first, HighlighterGroup{}});
            if (region.second.m_begin.empty() or region.second.m_end.empty())
                throw runtime_error("invalid regex for region highlighter");
        }
        if (not m_default_group.empty())
            m_groups.append({m_default_group, HighlighterGroup{}});
    }

    void highlight(const Context& context, HighlightFlags flags, DisplayBuffer& display_buffer, BufferRange range)
    {
        if (flags != HighlightFlags::Highlight)
            return;

        auto display_range = display_buffer.range();
        const auto& buffer = context.buffer();
        auto& regions = get_regions_for_range(buffer, range);

        auto begin = std::lower_bound(regions.begin(), regions.end(), display_range.first,
                                      [](const Region& r, ByteCoord c) { return r.end < c; });
        auto end = std::lower_bound(begin, regions.end(), display_range.second,
                                    [](const Region& r, ByteCoord c) { return r.begin < c; });
        auto correct = [&](ByteCoord c) -> ByteCoord {
            if (not buffer.is_end(c) and buffer[c.line].length() == c.column)
                return {c.line+1, 0};
            return c;
        };

        auto default_group_it = m_groups.find(m_default_group);
        const bool apply_default = default_group_it != m_groups.end();

        auto last_begin = (begin == regions.begin()) ?
                             ByteCoord{0,0} : (begin-1)->end;
        for (; begin != end; ++begin)
        {
            if (apply_default and last_begin < begin->begin)
                apply_highlighter(context, flags, display_buffer,
                                  correct(last_begin), correct(begin->begin),
                                  default_group_it->second);

            auto it = m_groups.find(begin->group);
            if (it == m_groups.end())
                continue;
            apply_highlighter(context, flags, display_buffer,
                              correct(begin->begin), correct(begin->end),
                              it->second);
            last_begin = begin->end;
        }
        if (apply_default and last_begin < display_range.second)
            apply_highlighter(context, flags, display_buffer,
                              correct(last_begin), range.second,
                              default_group_it->second);

    }

    bool has_children() const override { return true; }

    Highlighter& get_child(StringView path) override
    {
        auto sep_it = find(path, '/');
        StringView id(path.begin(), sep_it);
        auto it = m_groups.find(id);
        if (it == m_groups.end())
            throw child_not_found("no such id: "_str + id);
        if (sep_it == path.end())
            return it->second;
        else
            return it->second.get_child({sep_it+1, path.end()});
    }

    Completions complete_child(StringView path, ByteCount cursor_pos, bool group) const override
    {
        auto sep_it = find(path, '/');
        if (sep_it != path.end())
        {
            ByteCount offset = sep_it+1 - path.begin();
            Highlighter& hl = const_cast<RegionsHighlighter*>(this)->get_child({path.begin(), sep_it});
            return offset_pos(hl.complete_child(path.substr(offset), cursor_pos - offset, group), offset);
        }

        auto container = transformed(m_groups, IdMap<HighlighterGroup>::get_id);
        return { 0, 0, complete(path, cursor_pos, container) };
    }

    static HighlighterAndId create(HighlighterParameters params)
    {
        try
        {
            static const ParameterDesc param_desc{
                { { "default", { true, "" } } },
                ParameterDesc::Flags::SwitchesOnlyAtStart, 5
            };

            ParametersParser parser{params, param_desc};
            if ((parser.positional_count() % 4) != 1)
                throw runtime_error("wrong parameter count, expect <id> (<group name> <begin> <end> <recurse>)+");

            RegionsHighlighter::NamedRegionDescList regions;
            for (size_t i = 1; i < parser.positional_count(); i += 4)
            {
                if (parser[i].empty() or parser[i+1].empty() or parser[i+2].empty())
                    throw runtime_error("group id, begin and end must not be empty");

                Regex begin{parser[i+1], Regex::nosubs | Regex::optimize };
                Regex end{parser[i+2], Regex::nosubs | Regex::optimize };
                Regex recurse;
                if (not parser[i+3].empty())
                    recurse = Regex{parser[i+3], Regex::nosubs | Regex::optimize };

                regions.push_back({ parser[i], {std::move(begin), std::move(end), std::move(recurse)} });
            }

            auto default_group = parser.get_switch("default").value_or(StringView{}).str();
            return {parser[0], make_unique<RegionsHighlighter>(std::move(regions), default_group)};
        }
        catch (RegexError& err)
        {
            throw runtime_error(String("regex error: ") + err.what());
        }
    }

private:
    const NamedRegionDescList m_regions;
    const String m_default_group;
    IdMap<HighlighterGroup, MemoryDomain::Highlight> m_groups;

    struct Region
    {
        ByteCoord begin;
        ByteCoord end;
        StringView group;
    };
    using RegionList = Vector<Region, MemoryDomain::Highlight>;

    struct Cache
    {
        size_t timestamp = 0;
        Vector<RegionMatches, MemoryDomain::Highlight> matches;
        UnorderedMap<BufferRange, RegionList, MemoryDomain::Highlight> regions;
    };
    BufferSideCache<Cache> m_cache;

    using RegionAndMatch = std::pair<size_t, RegexMatchList::const_iterator>;

    // find the begin closest to pos in all matches
    RegionAndMatch find_next_begin(const Cache& cache, ByteCoord pos) const
    {
        RegionAndMatch res{0, cache.matches[0].find_next_begin(pos)};
        for (size_t i = 1; i < cache.matches.size(); ++i)
        {
            const auto& matches = cache.matches[i];
            auto it = matches.find_next_begin(pos);
            if (it != matches.begin_matches.end() and
                (res.second == cache.matches[res.first].begin_matches.end() or
                 it->begin_coord() < res.second->begin_coord()))
                res = RegionAndMatch{i, it};
        }
        return res;
    }

    const RegionList& get_regions_for_range(const Buffer& buffer, BufferRange range)
    {
        Cache& cache = m_cache.get(buffer);
        const size_t buf_timestamp = buffer.timestamp();
        if (cache.timestamp != buf_timestamp)
        {
            if (cache.timestamp == 0)
            {
                cache.matches.resize(m_regions.size());
                for (size_t i = 0; i < m_regions.size(); ++i)
                    cache.matches[i] = m_regions[i].second.find_matches(buffer);
            }
            else
            {
                auto modifs = compute_line_modifications(buffer, cache.timestamp);
                for (size_t i = 0; i < m_regions.size(); ++i)
                    m_regions[i].second.update_matches(buffer, modifs, cache.matches[i]);
            }

            cache.regions.clear();
        }

        auto it = cache.regions.find(range);
        if (it != cache.regions.end())
            return it->second;

        RegionList& regions = cache.regions[range];

        for (auto begin = find_next_begin(cache, range.first),
                  end = RegionAndMatch{ 0, cache.matches[0].begin_matches.end() };
             begin != end; )
        {
            const RegionMatches& matches = cache.matches[begin.first];
            auto& named_region = m_regions[begin.first];
            auto beg_it = begin.second;
            auto end_it = matches.find_matching_end(beg_it->end_coord());

            if (end_it == matches.end_matches.end() or end_it->end_coord() >= range.second)
            {
                regions.push_back({ {beg_it->line, beg_it->begin},
                                    range.second,
                                    named_region.first });
                break;
            }
            else
            {
                regions.push_back({ beg_it->begin_coord(),
                                   end_it->end_coord(),
                                   named_region.first });
                auto end_coord = end_it->end_coord();

                // With empty begin and end matches (for example if the regexes
                // are /"\K/ and /(?=")/), that case can happen, and would
                // result in an infinite loop.
                if (end_coord == beg_it->begin_coord())
                {
                    kak_assert(beg_it->begin_coord() == beg_it->end_coord() and
                               end_it->begin_coord() == end_it->end_coord());
                    ++end_coord.column;
                }
                begin = find_next_begin(cache, end_coord);
            }
        }
        cache.timestamp = buf_timestamp;
        return regions;
    }
};

template<typename Func>
HighlighterFactory simple_factory(const String id, Func func)
{
    return [=](HighlighterParameters params)
    {
        return HighlighterAndId(id, make_simple_highlighter(func));
    };
}

void register_highlighters()
{
    HighlighterRegistry& registry = HighlighterRegistry::instance();

    registry.append({
        "number_lines",
        { number_lines_factory,
          "Display line numbers \n"
          "Parameters: -relative, -hlcursor\n" } });
    registry.append({
        "show_matching",
        { simple_factory("show_matching", show_matching_char),
          "Apply the MatchingChar face to the char matching the one under the cursor" } });
    registry.append({
        "show_whitespaces",
        { simple_factory("show_whitespaces", show_whitespaces),
          "Display whitespaces using symbols" } });
    registry.append({
        "fill",
        { create_fill_highlighter,
          "Fill the whole highlighted range with the given face" } });
    registry.append({
        "regex",
        { RegexHighlighter::create,
          "Parameters: <regex> <capture num>:<face> <capture num>:<face>...\n"
          "Highlights the matches for captures from the regex with the given faces" } });
    registry.append({
        "regex_option",
        { create_regex_option_highlighter,
          "Parameters: <option name> <face>\n"
          "Highlight matches for the regex stored in <option name> with <face>" } });
    registry.append({
        "search",
        { create_search_highlighter,
          "Highlight the current search pattern with the Search face" } });
    registry.append({
        "group",
        { create_highlighter_group,
          "Parameters: <group name>\n"
          "Creates a named group that can contain other highlighters" } });
    registry.append({
        "flag_lines",
        { create_flag_lines_highlighter,
          "Parameters: <option name> <bg color>\n"
          "Display flags specified in the line-flag-list option <option name>\n"
          "A line-flag is written: <line>|<fg color>|<text>, the list is : separated" } });
    registry.append({
        "line_option",
        { create_line_option_highlighter,
          "Parameters: <option name> <face>\n"
          "Highlight the line stored in <option name> with <face>" } });
    registry.append({
        "ref",
        { create_reference_highlighter,
          "Parameters: <path>\n"
          "Reference the highlighter at <path> in shared highglighters" } });
    registry.append({
        "regions",
        { RegionsHighlighter::create,
          "Parameters: [-default <default group>] {<name> <begin> <end> <recurse>}..."
          "Split the highlighting into regions defined by the <begin>, <end> and <recurse> regex\n"
          "The region <name> starts at <begin> match, end at <end> match that does not\n"
          "close a <recurse> match. In between region is the <default group>.\n"
          "Highlighting a region is done by adding highlighters into the different <name> subgroups." } });
}

}